Wind turbines are an increasingly popular source of energy in the United States and Europe and in many other countries around the globe. In order to realize scale efficiencies in capturing energy from the wind, developers are erecting wind turbine farms having increasing numbers of wind turbines with larger turbines positioned at greater heights. In large wind turbine farm projects, for example, developers typically utilize twenty-five or more wind turbines having turbines capable of producing on the order of 1.2 Megawatts (MW) of power positioned at a height of fifty meters or higher above the ground. Providing wind turbines of these specifications typically provide scale efficiencies that reduce the cost of energy while making the project profitable to the developer. Placing larger turbines at greater heights enables each turbine to operate substantially free of boundary layer effects created through wind shear and interaction with near-ground irregularities in surface contours, e.g., rocks and trees. Greater turbine heights also lead to more steady operating conditions at higher sustained wind velocities, thereby producing, on average, more energy per unit time. Accordingly, there are economic and engineering incentives to positioning larger turbines at greater heights.
Positioning larger turbines at greater heights comes, however, with an added cost. The cost is associated with the larger and more massive towers that are required to withstand the additional weight of the larger turbines and withstand the wind loads generated by placing structures at the greater heights where wind velocities are also greater and more sustained.
An additional cost concerns the equipment that is required to erect the wind turbine. For example, the weight of conventional tube towers for wind turbines, e.g., towers having sectioned tube-like configurations constructed using steel or concrete—increases in proportion to the tower height raised to the 5/3 power. Thus, a 1.5 MW tower typically weighing 176,000 lbs at a standard 65 meter height will weigh approximately 275,000 lbs at an 85 meter height, an increase of about 56 percent. Towers in excess of 250,000 lbs, or higher than 100 meters, however, generally require specialized and expensive cranes to assemble the tower sections and to mount the turbine and blades on the assembled tower. Just the cost to transport and assemble one of these cranes needed to assemble a large tower and turbine can exceed $250,000 for a typical 1.5 MW turbine. In order to amortize the expense associated with such large cranes, wind turbine farm developers desire to pack as many wind turbines as possible onto the geographic area allocated to the towers and turbines, generally referred to as the “project footprint,” thereby spreading the crane costs over many wind turbine installations. However, with sites having limited footprints, developers are forced to amortize transport and assembly costs of the crane across fewer turbines, which may be economically unfeasible. Further, projects installed on rough ground require cranes to be repeatedly assembled and disassembled, which may also be economically unfeasible. Projects located on mountain top ridges or other logistically difficult sites may, likewise, be all but eliminated due to unfeasible economics, in addition to engineering difficulties associated with locating a crane at such sites.
In view of the forgoing, it will be appreciated that it would be an advantage over the previously available systems to be able to assemble high-elevation structural towers and to mount heavy wind turbines on the top of such towers without relying on relatively large and prohibitively expensive crane equipment. It would be another advantage over the previously available systems to provide an apparatus and method for assembling high elevation structural towers and mounting wind turbines on top of such assembled towers without the need for large and prohibitively expensive crane equipment. The illustrative embodiments described herein overcome these disadvantages as will become more apparent with an understanding of the below provided description.